Orthotic bracing systems generally lock or otherwise constrain joints. An orthosis may constrain any range of motion in an ankle, knee, hip, or other joint. A thoracic jacket typically inhibits motion in the torso. An orthosis or brace for a joint may be unlocked during periods of rest for the wearer, but an orthosis or brace for a body segment such as the torso generally remain fully locked while the individual wears the brace. Therefore, there is value in a torso bracing mechanism that would allow freedom of movement of the torso during periods of rest while varying the amount of resistance to movement of the torso depending on the activity of the individual donning the brace.
Ankle-foot orthotic braces (AFOs) are commonly used in the treatment of disorders that affect muscle function, such as stroke, spinal cord injury, muscular dystrophy, cerebral palsy, polio, and multiple sclerosis. AFOs can also be used to provide support to weak or wasted limbs. An AFO is externally applied, and is intended to manage the position and velocity of the ankle joint, compensate for weakness, and/or correct deformities. AFOs are also used to immobilize the ankle and lower leg in the presence of arthritis or fracture, and to correct foot slap and foot drag.
An AFO is not designed to provide power to move the ankle by itself. Rather, it is an assistive device that is intended mainly as a controller of the ankle joint angle throughout the gait cycle. Some AFOs assist with toe-off, essentially the last movement in the gait cycle on one side that propels an individual forward to take another step. By assisting the subject with toe-off, the AFO helps delay muscle fatigue due to this high intensity work. Some AFOs help to prevent foot-drop, which is an inability to fully dorsi-flex, and presents itself in two forms during gait, namely, toe-drag and foot-slap. Toe-drag happens when the toe is dragged on the floor during the swing phase of gait, which is problematic because the subject is more susceptible to tripping. To counteract toe-drag, the subject's gait has to be altered to raise the ankle higher in all gait situations. The other symptom, foot-slap, occurs after heel strike in the gait cycle, when the muscles cannot impede the torque about the ankle and the foot literally and uncontrollably slaps the floor, which can injure the subject after repeated cycles.
One example of an AFO uses artificial pneumatic muscles because of their ability to mimic, both in control and power output, real muscles. One weakness of artificial muscles, however, is their power source, i.e., compressed air. To develop the torque needed for an AFO, the air compressor and other necessary components must be bulky and heavy. Another weakness is the pull-only actuation style, requiring either opposed pairs of pneumatic cylinders to produce both plantar and dorsi flexion or an opposing spring element to produce dorsi flexion.
Although AFOs exist that either assist or control dorsi flexion or plantar flexion, there is a need for an apparatus capable of providing both dorsi flexion and plantar flexion assistance. Accordingly, there is a need for an orthotic device for joint that provides variable resistance to movement of the joint.